This invention relates to powering of kinescopes, and more particularly to focus tracking in the presence of ultor voltage variation.
Video displays, such as are used for television viewing and computer operation, often use kinescopes, picture tubes, or cathode ray tubes (CRTs) as the display device. A picture tube is a vacuum tube which has a phosphorescent display screen and control terminals for directing a focussed electron beam toward the screen to generate the desired image. In general, a picture tube requires a relatively high anode or xe2x80x9cultorxe2x80x9d voltage to accelerate the electron beam toward the screen, a cathode and a grid which coact for modulating the intensity of the electron beam in accordance with the image to be generated, and a focus electrode to which a focus voltage is applied to cause the electron beam to be focussed at the screen. In addition, a picture tube is associated with a deflection arrangement for deflecting the electron beam both vertically and horizontally. The ultor or anode voltage of the picture tube is often regulated in order to reduce voltage changes attributable to interaction between the internal impedance of the ultor voltage source and the varying cathode or beam current required to generate an image. xe2x80x9cStaticxe2x80x9d focus voltage is applied to the focus terminal of the picture tube in order to focus the electron beam at a given location, such as the center of the screen. It is well understood that the value of the xe2x80x9cstaticxe2x80x9d focus voltage is desirably a fixed proportion of the ultor voltage. Dynamic focus control is often provided for adjusting the value of the focus voltage applied to the picture tube in accordance with the position of the electron beam, in order to keep the electron beam focussed on the screen notwithstanding the changing length of the electron beam path attributable to deflection.
A video imaging apparatus according to an aspect of the invention comprises a first cathode-ray tube having a first ultor electrode and a first focus electrode, and a second cathode-ray tube having a second ultor electrode and a second focus electrode. A power supply for generating an ultor voltage is coupled to the first and second ultor electrodes. The ultor voltage may have a fluctuating voltage component produced by beam current variations. A high voltage amplifier generates a dynamic focus voltage component at a frequency related to a deflection frequency. A combining network combines the fluctuating voltage component and the dynamic focus voltage component to develop a combined, dynamic focus voltage. The combined, dynamic focus voltage is coupled to each of the first and second focus electrodes for developing from the combined, dynamic focus voltage each of a first dynamic focus voltage at the first focus electrode and a second dynamic focus voltage at the second focus electrode.
According to another aspect of the invention, a video imaging apparatus comprises a first cathode-ray tube having a first ultor electrode and a first focus electrode, and a second cathode-ray tube having a second ultor electrode and a second focus electrode. A power supply generates an ultor voltage coupled to the first and second ultor electrodes having a fluctuating voltage component produced by beam current variations. A high voltage amplifier generates a dynamic focus voltage component at a frequency related to a deflection frequency. A combining network combines the fluctuating voltage component and the dynamic focus voltage component to develop a combined, dynamic focus voltage. A first voltage divider is responsive to the combined, dynamic focus voltage for developing from the combined, dynamic focus voltage a first dynamic focus voltage at the first focus electrode, and a second voltage divider is responsive to the combined, dynamic focus voltage for developing from the combined, dynamic focus voltage a second focus voltage at the second focus electrode.
A video imaging apparatus according to another aspect of the invention comprises a first cathode-ray tube having a first ultor electrode and a first focus electrode, and a second cathode-ray tube having a second ultor electrode and a second focus electrode. A power supply for generating an ultor voltage is coupled to the first and second ultor electrodes. The ultor voltage may have a fluctuating voltage component produced by beam current variations. A high voltage amplifier generates a dynamic focus voltage component at a frequency related to a deflection frequency. A combining network combines the fluctuating voltage component and the dynamic focus voltage component to develop a combined, dynamic focus voltage. The combined, dynamic focus voltage is coupled to each of the first and second focus electrodes for developing from the combined, dynamic focus voltage each of a first dynamic focus voltage at the first focus electrode and a second dynamic focus voltage at the second focus electrode.
According to yet another aspect of the invention, a video imaging apparatus comprises a first cathode-ray tube having a first ultor electrode and a first focus electrode, and a second cathode-ray tube having a second ultor electrode and a second focus electrode. A power supply generates an ultor voltage coupled to the first and second ultor electrodes having a fluctuating voltage component produced by beam current variations. A high voltage amplifier generates a dynamic focus voltage component at a frequency related to a deflection frequency. A combining network combines the fluctuating voltage component and the dynamic focus voltage component to develop a combined, dynamic focus voltage. A first voltage divider is responsive to the combined, dynamic focus voltage for developing from the combined, dynamic focus voltage a first dynamic focus voltage at the first focus electrode, and a second voltage divider is responsive to the combined, dynamic focus voltage for developing from the combined, dynamic focus voltage a second focus voltage at the second focus electrode.